Method for depositing a film

ABSTRACT

An apparatus for depositing a film at atmospheric pressure and a method used for this formation are offered. Radicals are produced inside a space in which an electric discharge is induced. This space is shrouded in a purge gas to isolate the space from the outside air, for preventing the radicals traveling to the surface of a substrate from being affected by the outside air. A magnetic field and a bias voltage are made to act on the produced plasma, so that the radicals can reach the substrate surface with greater ease. The arriving radicals promote the formation of the film on the surface of the substrate.

This application is a continuation of Ser. No. 07/803,217, filed Dec. 6,1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus fordepositing a film substantially at atmospheric pressure. The inventionis, therefore, capable of offering an inexpensive film formationapparatus which does not need any evacuating apparatus such as a vacuumpump. The film can be made from hard carbon, silicon nitride, siliconoxide, or other similar material. Films of this kind can be used toharden or improve the surface of plastic, glass, or organicphotosensitive body or to prevent reflection at such surface. Thesefilms can find wide application. The invention is intended to provide amethod and an apparatus for mass-producing these films at low costs.

2. Prior Art

Presently, coatings made of materials having unconventional functionssuch as hard carbons, silicon nitride, and silicon oxide are oftenformed by plasma chemical vapor deposition (PCVD). Most PCVD processesutilize reduced pressure. The main advantages of the use of reducedpressure are: (1) The effects of impurities contained in the atmospheresuch as oxygen can be eliminated; (2) Where a plasma is employed, astable glow discharge is obtained over a wide region; (3) Since the meanfree path is long, the film thickness uniformity and the step coveragecan be easily improved. However, an expensive evacuating apparatus and avacuum vessel that is strong enough to withstand vacuum are needed toobtain reduced pressure (vacuum).

Generally, even a trace amount of impurity contamination is nottolerated in the field of semiconductor technologies since the coatingsmust have high performance. High depreciation costs of equipment can beeasily assigned to commercial products having high added values. Forthese reasons, these coatings have been fabricated by plasma chemicalvapor deposition as described above. On the other hand, where coatingsare formed for hardening or improvement of surface of plastic, glass, ororganic photosensitive body, or for prevention of reflection at suchsurface, very high purities are not required. Rather, increased costsdue to the usage of expensive equipment present problems. That is, thebest compromise must be struck between performance and cost.

Plasma CVD processes that need no evacuating apparatus are known. Aplasma CVD which is applied to etching is described in Japanese PatentApplication No. 286883 filed in 1990. In particular, a space is filledwith a flowing gas consisting mainly of helium at a pressure close toatmospheric pressure. An AC electric field is applied to the space toionize the gas and a halogenated etching gas added to it. In this way,excitons are produced and used for etching. Also, a technique making useof an electric discharge of a gas consisting mainly of helium fordeposition of a thin film is known (the 2nd Volume of the Manuscriptsfor the 37th Japanese Applied Physics-Related Combined Lecture Meeting,28p-ZH-10). However, in this technique, the reaction space is requiredto be replaced with a gas consisting mainly of helium and, therefore,the space must be once evacuated to a vacuum.

As described previously, the conventional coating formation process atreduced pressure is too expensive only for the hardening of the surfaceof plastic, glass, or organic photosensitive body or for formation of acoating. Therefore, more economical methods are being sought. Acontemplated, economical coating formation method exploits an electricdischarge at atmospheric pressure. This method yields the followingadvantages: (1) Since vacuum evacuation is not needed, an expensiveevacuating system is not necessitated; (2) The time heretofore taken toevacuate the space can be omitted and so the processing time can beshortened; and (3) Since the coating is formed at high pressure, thecollision time is short and the reaction rate is high, so that theprocessing time can be shortened. These can make the coating formationapparatus cheaper and shorten the processing time and hence contributegreatly to reductions in the costs of coating formation.

Formation of a coating at atmospheric pressure poses three problems. Thefirst problem is contamination with atmospheric components.Specifically, ions, radicals, and other matter are produced in the spacein which an electric discharge is induced. When they are beingtransported to the surface of the substrate on which the coating isformed, they react with impurities in the atmosphere, especially oxygen,thus affecting the coating. Since the surface on which a coating isbeing formed is active, the impurities adhering to the surface such asoxygen will deteriorate the performance of the coating.

The second problem is that the electric discharge space is limited to anarrow region. Generally, where a coating is formed on a substrate, itis required that the coating be created uniformly over a large area. Forthis purpose, a plasma must be generated over a wide area. Where anelectric discharge is produced at atmospheric pressure, the mean freepath of particles is as short as less than 1 μm. Therefore,recombination due to collision of electrons with ions in the space takesplace frequently. Sometimes, the electric discharge region cannot beusually extended to over several millimeters.

The third problem is that the reaction rate is too high. In particular,ions and radicals collide with high probability and so reactions occurinside the space before the coating is grown on the substrate surface.As a result, they deposit as powder on the substrate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method fordepositing a film free of the foregoing problems.

It is another object of the present invention to provide an apparatusfor depositing an improved film substantially at atmospheric pressure.

In accordance with the present invention, a method for depositing a filmcomprises the steps of:

forming a reaction space which is substantially kept airtight by forminga shield gas flow intervening between said reaction space and atmosphereoutside said reaction space;

introducing helium gas and a reaction gas material into said reactionspace;

activating said reaction gas material by glow or corona discharge by theuse of an electromagnetic energy in said reaction space; and

depositing the activated material on a substrate.

The reaction gas material is activated directly by the electromagneticenergy. Alternatively, the helium gas is activated to an exciton by theelectromagnetic energy and the reaction gas material is activated by anenergy of said exciton.

In accordance with the present invention, an apparatus for depositing afilm comprises:

a shield gas nozzle;

a reaction space which is substantially kept airtight during operationthereof by forming a shield gas flow intervening between said reactionspace and atmosphere outside of said reaction space from said purge gasnozzle;

a central electrode provided in said reaction space;

a peripheral electrode provided around said central electrode;

an insulator provided between said central electrode and said peripheralelectrode;

a first power source for supplying to said reaction space anelectromagnetic energy required to maintain discharge in said reactionspace; and

a second power source for applying an electric field between saidcentral electrode and a substrate to be coated in order to make a plasmaion in said reaction space attracted by said substrate.

It is preferred that the deposition of a film is carried out with thesurface to be coated sputtered by a bias application. It is alsopreferred that a magnetic field is applied to the reaction space in sucha way that various particles inside the resulting plasma are attractedtoward the substrate. The particles may be rotated by the magneticfield.

The novel method for depositing a film is carried out substantially atatmospheric pressure to attain a cost reduction. This method ischaracterized in that it uses no evacuating apparatus. An electricdischarge at atmospheric pressure must satisfy the three conditions: (1)The electric discharge space is permeated with helium; (2) An insulatoris inserted in at least one location in the electric discharge path; and(3) The frequency of the power supply for exciting the electricdischarge is in excess of tens of kilohertz.

Of these conditions, the gas of the condition (1) forming a gaseousenvironment, or an atmosphere, is of importance. The gaseous rawmaterial of the film is added to this gas forming the atmosphere. Theratio of the raw material gas to the helium is 5% or less, preferably 1%or less. If the ratio is in excess of 5%, then the electric discharge isunstable. If the ratio exceeds 1%, then a large amount of powder isproduced.

The raw material gas is selected according to the kind of the formedfilm. Where a hard carbon film is formed, the raw material gas isselected from hydrocarbon gases, such as methane, ethylene, acetylene,benzene, and methylbenzene, halogenated carbons, such as carbontetrafluoride, carbon tetrachloride, fluorobenzene, and chlorobenzene,halogenated hydrocarbon gases, and alcohols, such as ethanol andmethanol. In essence, any gas can be used as long as some degree ofvapor pressure is produced at 1 atm. at room temperature. However,harmless gases such as methylbenzene, chlorobenzene, and ethanol arepreferable to harmful materials such as acetylene and benzene, becausethe component of the raw material gas which has not reacted is expelledinto the air. Since a molecule having more carbons tends to provide ahigher reaction rate, ethylene is preferable to methane, and acetyleneis preferable to ethylene. Aromatic compounds such as benzene are morepreferable. Furthermore, the rate at which a film is formed is highwhere the raw material gas contains a halogen element, because a halogenelement such as fluorine acts like a catalyst. In particular, thehalogen element pulls out the hydrogen of a hydrocarbon molecule forexample in the form of HF. Thus, the hydrocarbon molecule is easilyactivated. Halogen elements can be supplied as a molecule combined withcarbon such as carbon tetrafluoride, carbon tetrachloride,fluorobenzene, and chlorobenzene, and also as any of nitrogentrifluoride, sulfur hexafluoride, tungsten hexafluoride, and fluorinegas. Where a gas containing a group III or V element such as nitrogen,boron, or phosphorus is added to the raw material gas, hard carbon filmsshow slight electrical conductivity. This is effective in suppressingelectrostatic electricity. For instance, if nitrogen trifluoride isadded to a hydrocarbon gas such as ethylene or methylbenzene, asemi-insulative, i.e., electrostatic electricity-preventing, hard carbonfilms can be deposited at high rates. If hydrogen is added to the rawmaterial gas, then dangling bonds in the hard carbon film are terminatedby hydrogen. Also, sp and sp² bonds which have not reacted easily formsp³ bonds by the action of hydrogen. Consequently, the hard carbon filmsbecome harder, and their transparency increases.

Where the formed film is made of silicon nitride, silane gas, disilanegas, and a nitrogen source such as nitrogen gas or ammonia gas can beused as the raw material gas. Where the formed film is made of siliconoxide, silane gas, disilane gas, oxygen, N₂ O, or other gas can be used.

It is possible to add a rare gas such as helium, argon, or xenon, to theraw material gas to reduce the probability of collision with thepresently reacting preform of the film, thus suppressing generation ofpowder. For the same purpose, hydrogen gas can be employed as a buffergas.

The raw material gas selected as described above is adjusted to apressure slightly higher than 1 atm. by a pressure governor. The gas ismixed with helium whose pressure is similarly adjusted. Then, themixture gas is introduced into a reaction space substantially atatmospheric pressure, preferably 700 to 900 torr. One or more electrodesare provided in the reaction space. A shield (peripheral electrode) isdisposed outside the electrodes. An insulator is mounted between theshield and the electrodes. An AC electric field of a frequency of 20 kHzor more is applied between the shield and each electrode to produce aplasma between each electrode and the shield with the insulatorinterposed between them. The plasma is generated by a glow discharge orcorona discharge. The insulator and the frequency of 20 kHz or more areused to prevent arc discharge. If a large amount of electric power issupplied at a low frequency, then an arc discharge will occur. If an arcdischarge takes place, the electrodes and the insulator will be damaged.Also, the electron temperature will drop. As a result, a normal coatingwill not be formed. One method of supplying electric power withoutshifting to an arc discharge is to increase the power supply frequency.This is identical in principle with supply of a large electric power toan RF corona. Specifically, a current of an RF power flows through theelectrostatic capacitance of the space and an effective electric powerin the RF power is consumed in a plasma which is equivalent to aresistor connected to the electrostatic capacitance of the space inseries, as expressed in terms of an equivalent circuit. For instance, ata frequency of 13.56 MHz, an effective electric power of about 100 W canbe stably supplied. At this time, the volume of the electric dischargespace is about 20 mm³. If the frequency is increased up to the microwaverange, then the electric power will be supplied at higher efficiency.However, if the wavelength is as short as tens of centimeters to severalcentimeters, the power must be handled as electromagnetic waves.Therefore, contrivances are required for the waveguides and theelectrodes. In this case, the electric discharge space itself must beregarded as a lossy waveguide, and the shape and the material must be soselected that the impedance is matched, for preventing reflection atevery junction.

The electric power supplied for the electric discharge may be RF wavesmodulated with pulses or rectangular waves. If the duty cycle is 50% orless, then the plasma produced at the beginning of the electricdischarge becomes different in nature with the plasma sustained bycontinuous electric discharge, because the effect of the afterglow isconspicuous. At the beginning of the electric discharge, the plasma hasa high impedance and, therefore, a high voltage is applied to the space.(We are not sure whether it can be referred to as a plasma in thetransient phase of the beginning of the electric discharge, but it isassumed that a plasma is started to be produced when a discharge currentexceeding the dark current flows.) That is, the energy that each oneelectron inside the plasma possesses is large, and the electrontemperature is high. At this time, the raw material gas existing insidethe plasma space is efficiently excited. The plasma becomes an afterglowwhen the electric power subsequently ceases to be supplied. At thistime, the external electric field applied to the space is no longerpresent; only an internal electric field exists in the space. Thisinternal electric field also quickly disappears because of recombinationof ions with electrons inside the afterglow. If a continuous electricdischarge is produced, the electric field will be concentrated in minuteprotrusions on the surface of the substrate, thus causing selectivegrowth of a film. This will result in pinholes or voids. On the otherhand, during afterglow discharge, the electric field is not concentratedin the minute protrusions on the surface of the substrate and,therefore, a good film free of pinholes or voids is formed. That is,activated clusters, or the preform of a film, are allowed to adhereuniformly to the surface of the substrate by the use of radio-frequencywaves modulated with pulses or rectangular waves. Hence, a good coatingcan be grown at a high speed. The pulse duration is preferably set equalto the time for which the afterglow persists, or on the order of severalmilliseconds.

The simplest form of the electric discharge space according to theinvention is a cylinder. In particular, a cylindrical insulator ismounted between a grounded cylindrical peripheral (outer) electrode anda columnar central electrode disposed in the center of the space insidethe peripheral electrode. The cylindrical insulator, the columnarcentral electrode and the cylindrical peripheral electrode may bearranged coaxially with one another. An AC electric field is appliedbetween the central electrode and the peripheral electrode to produce aplasma in the gap between the insulator and the central electrode. Thisgap is 5 mm or less, preferably 1 mm or less. It could be said that thiscylindrical structure resembles a point light source. If it is notmoved, a dotted coating will be formed on the surface of a substrate.Therefore, in order to deposit a film uniformly over a wide region onthe substrate, it is necessary to move the substrate or the filmformation apparatus. Where the substrate is a plane, a two-axis driversuch as an XY table is used. If a further axis is added, i.e., an XYZtable, and if the system is controlled by a computer or the like, thecoating can be shaped into any desired curved surface.

Other geometries include a straight form and a doughnut form. A straightelectric discharge apparatus can be realized by an array of cylindricalapparatuses of the above-described structure. Alternatively, a gap of 5mm or less, preferably 1 mm or less, may be formed in a straightelectrode between an insulator and a grounded outer (peripheral)electrode. This gap is used as a straight electric discharge space.Where the substrate is a plane and a straight electric dischargeapparatus is used, either the substrate or the film formation apparatusneeds to be moved only along one axis. Where the substrate takes theform of a drum, a doughnut film formation apparatus may beadvantageously used. This doughnut film formation apparatus can befabricated by closing both ends of the aforementioned straight electricdischarge apparatus.

Non-oxidizing gases can be used as a shield gas. Typical examplesinclude nitrogen, argon, helium, and krypton. The used gas acts toisolate the electric discharge region from the constituents of the air,especially oxygen, for preventing the constituents of the air fromentering the film formed by electric discharge. The shield gas isintroduced in such a way that the electric discharge region is shroudedin this gas. As an example, in the case of formation of theabove-described dotted coating, an outlet nozzle or port is disposedoutside the peripheral (outer) electrode so as to surround it. A shieldgas is admitted in such a manner that the electric discharge region isshrouded in the gas. At this time, the amount of the introduced purgegas is considerably larger than the electric discharge atmosphere gas.The shield gas should be supplied at a high pressure to prevent theshield gas itself from causing an electric discharge.

The generation of powder that is a problem with the prior art electricdischarge at atmospheric pressure is due to excessive growth of clustersin air before they are conveyed to the surface of the substrate. Toprevent this, any of various countermeasures must be taken. For example,the reaction rate in air is reduced. Ions, radicals, or clusters aretransported positively to the surface of the coating. The reaction rateat the surface of the substrate is increased. For these purposes, theeffects of a magnetic field are utilized, or a bias voltage is appliedto the substrate.

In order to ensure that the active species produced by electricdischarge at atmospheric pressure inside the plasma shrouded in theelectric discharge atmosphere are conveyed to the substrate on which afilm is formed, a bias electric field is applied to the substrate. Also,a magnetic field is applied to the plasma produced by the electricdischarge. Various methods are available to apply a magnetic field tothe plasma. For example, a conventional permanent magnet may be disposedon the rear surface of the substrate on which a film is formed, thesubstrate being located opposite to the electric discharge apparatus, ora solenoid coil is mounted near the electric discharge region producedby the electric discharge apparatus to apply a magnetic field thereto. Acombination of these techniques is also possible. In any case, thedirection of the magnetic field set up by a magnetic field-generatingmeans is so selected as to ensure that the active species in the plasmaof the electric discharge atmosphere gas produced by an electricdischarge at normal pressure are conveyed to the substrate on which afilm is formed. The key role of the magnetic field applied to the plasmais to bring radicals having spins, electrons, and ionized active speciesto the surface of the substrate on which a film is formed. As a result,the density of the active species around the substrate surface isenhanced. It is desired to make the strength of the magnetic field ashigh as possible. The strength is 200 gauss or more, preferably 500gauss or more in the electric discharge region (reaction space).

One method of applying a bias electric field to the substrate is toapply a bias between the substrate and the electric discharge electrodeby means of a DC or RF power supply. The active ions in the plasma areattracted toward the substrate by the bias electric field. The densityof high energy ions is increased in the vicinities of the substrate. Theraw material gas receives energy from these ions, thus increasing thedensity of the radicals near the substrate.

The bias electric field causes the ions to collide against thesubstrate. Energy is given to the substrate from the ions by thecollision. The portion of the substrate which is quite close to itssurface becomes hot to improve the adhesion of the coating (film) to thesubstrate. Also, the reaction occurring at the surface of the substrateto form a film is accelerated. That is, the ions moved to the substrateby the bias electric field function similarly to heating of the base. Asthe distance between the substrate and the electric discharge electrodevaries, the effect of the electric field applied to the substratechanges greatly. Therefore, it is necessary to maintain the distancebetween the substrate and the electrode constant at all times. As aconsequence, a distance-measuring instrument and a distance controlmechanism are needed.

It is necessary that the frequency of the bias electric field be lowerthan the ion plasma frequency determined by the ion density inside theplasma. If this requirement is satisfied, the ions are oscillated by thebias electric field. The kinetic energy is transmitted to the substrate.Generally, the appropriate value of the frequency of the bias field is 1MHz or less.

These techniques ensure that the radicals produced inside the space aretransported to the surface of the substrate. Also, the reaction at thesurface of the substrate is promoted. The result is that a dense filmhaving little powder, i.e., free of pinholes, is deposited at a highrate.

Other objects and features of the invention will appear in the course ofthe description thereof which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a film formation apparatus havingcoaxial cylinders according to the invention, and in which gas andelectrical systems are also shown;

FIG. 2 is a perspective view of an apparatus for depositing a film on acylindrical substrate, the apparatus being fabricated in accordance withthe invention; and

FIG. 3 is a cross-sectional view of the electric discharge portion ofthe apparatus shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

Referring to FIG. 1, there is shown an apparatus for forming dots toproduce a coating in accordance with the invention. Gas and electricalsystems are also shown in FIG. 1. A cylindrical insulator 2 and a shieldgas nozzle 3 are mounted coaxially with a columnar central conductor(electrode) 1, which is held to an insulating support 4. The centralconductor 1 and the nozzle 3 are made of stainless steel. The insulator2 is made of quartz glass. The insulating support 4 is made of Teflon.The shield gas nozzle 3 consists of two coaxial cylinders and has aneject port 6. A shield gas is introduced between the two cylinders ofthe nozzle 3 at about 1 atm. and ejected from the eject port 6. Thiseject port 6 is directed outward so that the gas may be emitted towardthe outer circumference. An electric discharge takes place between thecentral conductor 1 and the cylindrical insulator 2 to produce radicals.The resulting radicals are conveyed toward a substrate 71 by the flow ofthe gas. The present invention is characterized in that a solenoid 61and a permanent magnet 62 are mounted on the outer surface of theapparatus and on the back side of a substrate holder 70, respectively,to draw the radicals along the magnetic flux toward the substrate 71.The outside diameter of the central conductor 1 is 1 mm. The cylindricalinsulator 2 has an inside diameter of 1.7 mm and an outside diameter of2.5 mm. The space in which the electric discharge is produced is 20 mmlong.

The substrate 71 is made of polycarbonate and place on the substrateholder 70 made of stainless steel that is a paramagnetic substance. Thesubstrate 71 is not positively heated. The distance between the end ofthe electric discharge space and the surface of the substrate is 1 mm.

A raw material gas is supplied from a raw material gas bomb 11 via apressure governor 21, a stop valve 31, and a flow controller 41. Thepressure of the gas supplied from the bomb 11 is adjusted by thegovernor 21. The flow rate of the raw material gas is controlled by theflow controller 41. Similarly, helium gas is supplied from a helium gasbomb 12 via a pressure governor 22, a stop valve 32, and a flowcontroller 42. The pressure of the helium gas supplied from the bomb 12is adjusted by the governor 22. The flow rate of the helium gas iscontrolled by the flow controller 42. The raw material gas and thehelium gas are mixed and supplied into the electric discharge space. Theraw material bomb 11 is filled with 10% methane gas balanced withhydrogen gas. Ninety nine (99) parts of the helium gas and 1 part of theraw material gas are mixed. The total flow of the mixture gas is 100sccm.

Electric power, e.g. alternating voltage, is supplied to the centralconductor 1 from a high frequency (radio-frequency) power supply 51 viaa blocking capacitor 53. The power supply frequency is 13.56 MHz. Theeffective electric power supplied is 20 W. In one feature of theinvention, a bias voltage is applied from a bias power supply 52 via afirst high frequency (radio-frequency) stopping coil 55 and a secondhigh frequency (radio-frequency) stopping coil 56. The high frequency(RF) electric power transmitted through the first coil 55 is permittedto escape by a bypass capacitor 54. As a result, the bias power supply52 is protected. In the present example, the applied bias voltage is DCvoltage. The voltage is -100 V with respect to the substrate holder.

A shield gas is supplied into the shield gas nozzle from a bomb 13 via apressure governor 23, a stop valve 33, and a flow controller 43. Thepressure of the gas supplied from the bomb 13 is adjusted by thegovernor 23. The flow rate of the shield gas supplied into the shieldgas nozzle is controlled by the flow controller 43. In the presentexample, nitrogen is used as the shield gas. The flow rate is 1000 sccm.

A hard carbon film was formed on a substrate made of polycarbonate withthe above-described apparatus by the method described above. Althoughthe film was grown at a very high rate that was 0.2 μm/min. just underthe opening of the electric discharge region, little powder wasproduced. The film was good in quality, since only a small amount ofpinholes existed. The hardness measured with a microhardness tester wasabout 3000 kgf/mm². The measured spectral transmittance in the visiblerange was in excess of 90%, i.e., almost transparent. Measurements usingFT-IR (Fourier-transform infrared spectrometry) and Raman spectroscopyhave shown that the ratio of sp³ bond to sp² bond was 1.6:1, which isclose to the ratio of the bonds in diamond.

In the present example, the film formation apparatus was not moved.Obviously, a uniform film can be formed on a substrate surface having alarge area by scanning the surface at a constant speed.

COMPARATIVE EXAMPLE 1

The present example was similar to Example 1 except that no magneticfield was developed. The hardness and the transmittance of the filmformed by this method were almost identical to those of Example 1, butthe deposition rate was lower slightly. Also, much powder was observed.

COMPARATIVE EXAMPLE 2

The present example was similar to Example 1 except that no bias voltagewas applied. The film formed by this method had a lower hardness and ahigher transmittance than the film of Example 1. Much powder wasobserved in the same way as in Comparative Example 1. The depositionrate was not different.

COMPARATIVE EXAMPLE 3

The present example was similar to Example 1 except that no shield gaswas used. Only a slight amount of coating was formed just under theopening of the electric discharge region by this method. The depositionrate decreased by a factor of approximately ten. We consider that thisdecrease is due to etching of the portion of the coating which is closeto the outer fringe, the etching being allowed by addition of oxygen.Neither the hardness nor the transmittance changed.

EXAMPLE 2

This example is intended to form a hard carbon film on a cylindricalsubstrate. The appearance of the used apparatus is shown in FIG. 2. Theapparatus comprises a frame 4, an elevating mechanism 3 mounted to theframe 4, and a film formation apparatus 2 held to the elevatingmechanism 3. A cylindrical substrate 1 is disposed inside the filmformation apparatus 2. The electric discharge opening inside the filmformation apparatus faces inward to form a film on the surface of thesubstrate. The elevating mechanism 3 moves vertically at a uniformvelocity corresponding to the deposition rate. The substrate and thefilm formation apparatus are shown in FIG. 3 in cross section. Theapparatus has an electric discharge electrode 1, an insulator 2, ashield nozzle 3, and an electrode support 4. That is, the apparatus isessentially identical with the apparatus of Example 1. Produced radicalsare conveyed to the surface of a substrate 70 by a magnet 61. The ratioof the raw material gas to the helium gas, the flow rate of the mixturegas, the power supply frequency, and the bias voltage were the same asthose of Example 1. The electric power supplied was 2 W/mm. Where thecircumference was 40 mm, the electric power was 80 W. Thecharacteristics of the obtained film such as the hardness, thetransmittance, the ratio of the sp³ bond to the sp² bond, and thedeposition rate, were almost identical with those obtained in Example 1.No powder was observed.

As described above, in accordance with the present invention, a gasconsisting mainly of helium is caused to produce an electric dischargeat atmospheric pressure. A gaseous raw material is added to the gas.Where a hard carbon film is formed, the raw material is methane,hydrogen, or other substance. The electric discharge is shrouded innitrogen gas or other shield gas. A magnetic field and a bias voltageare applied. A coating of high quality can be deposited at a high ratewithout producing powder.

What is claimed is:
 1. A method for depositing a film comprising thesteps of:forming a reaction space by flowing a shield gas interveningbetween said reaction space and atmosphere outside said reaction space;introducing carrier gas and a reactive gas into said reaction space;activating said reactive gas by glow or corona discharge by the use ofan electromagnetic energy in said reaction space; and depositing theactivated material on a substrate.
 2. The method of claim 1 wherein saidreactive gas is activated directly by said electromagnetic energy. 3.The method of claim 1 wherein said carrier gas ia activated to anexciton by said electromagnetic energy and said reactive gas isactivated by an energy of said exciton.
 4. The method of claim 1 whereinsaid shield gas flow is formed toward said substrate in order that saidsubstrate is in contact with said reaction space and serves to keep saidreaction space substantially airtight together with said shield gasflow.
 5. The method of claim 1 wherein the introduction of said carriergas and said reactive gas is carried out substantially at atmosphericpressure in terms of total pressure thereof in said reaction space. 6.The method of claim 1 wherein a magnetic field is applied to saidreaction space in order to rotate said material thereby.
 7. The methodof claim 6 wherein said magnetic field is 200 Gauss or more in saidreaction space.
 8. The method of claim 1 wherein a halogen containinggas is further introduced into said reaction space as catalyst duringsaid introducing step in case of carbon film formation.
 9. The method ofclaim 1 wherein a gas selected from the group consisting of helium,argon, xenon and hydrogen is further introduced into said reaction spaceduring said introducing step in order to suppress generation of powder.10. The method of claim 1 wherein said reactive gas comprises ahydrocarbon gas.
 11. The method of claim 1 wherein a central columnarelectrode is provided in said reaction space and a grounded peripheralcylindrical electrode is provided around said central electrode and acylindrical insulator is provided therebetween and coaxial with saidcentral electrode and said peripheral electrode and said electromagneticenergy is supplied to said reaction space by applying an alternatingvoltage to said central electrode.
 12. The method of claim 11 whereinfrequency of said alternating voltage is 20 KHz or more.
 13. The methodof claim 1 wherein a shield gas of said shield gas flow is an inactivegas selected from the group consisting of nitrogen, argon and helium.14. The method of claim 1 wherein the introduction of said carrier gasand said reactive gas is carried out at a pressure of 700 to 900 torr interms of total pressure thereof in said space.
 15. The method of claim 1wherein said reaction space is substantially kept airtight.
 16. Themethod of claim 1 wherein said carrier gas is helium.
 17. A plasmaprocessing method comprising the steps of:preparing a central columnarelectrode and an outer electrode around said central columnar electrodein a coaxial relation such that a discharge space is formedtherebetween; placing a dielectric member between said central columnarelectrode and said outer electrode; introducing a reactive gas from oneend of said discharge space; applying a high frequency voltage betweensaid central columnar electrode and said outer electrode to form aplasma of said reactive gas; directing said plasma to a surface of anobject through another end of said discharge space in order to treatsaid surface with said plasma, flowing a shield gas to prevent saidplasma from directly contacting the air.
 18. The method of claim 17wherein said shield gas is applied from a nozzle surrounding said outerelectrode.
 19. The method of claim 17 wherein said high frequencyvoltage is pulsed.
 20. The method of claim 17 further comprising thestep of applying bias voltage to said central electrode.
 21. The methodof claim 17 further comprising applying a magnetic field to said plasma.